Piezoelectric element, piezoelectric sensor, electronic device, and method for manufacturing piezoelectric element

ABSTRACT

A piezoelectric element includes a support body having a displacing part capable of undergoing displacement, a lower electrode layer having a lower main electrode body and a lower electrode wire part with the lower main electrode body being formed on the support body and provided within the displacing part in a plan view and the lower electrode wire part being connected to the lower main electrode body and provided across an interior and an exterior of the displacing part, a first piezoelectric layer provided on the lower main electrode body, an upper electrode layer provided across the interior and exterior of the displacing part with at least a part of the upper electrode layer being layered on the first piezoelectric layer and insulated from the lower electrode layer, and a second piezoelectric layer provided on the support body to cover at least a part of the lower electrode wire part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2010-054168 filed on Mar. 11, 2010 and Japanese Patent Application No.2010-284662, filed on Dec. 21, 2010. The entire disclosures of JapanesePatent Application Nos. 2010-054168 and 2010-284662 are herebyincorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a piezoelectric element in which apiezoelectric body is formed on a thin film, a piezoelectric sensorprovided with the piezoelectric element, an electronic device, and amethod for manufacturing a piezoelectric element.

2. Related Art

Conventionally, there have been known piezoelectric elements (i.e.,ultrasound elements) in which piezoelectric bodies are layered onsupporting films and the piezoelectric bodies are subjected to a voltageand caused to vibrate, whereby the supporting films are caused tovibrate and ultrasound is produced (e.g., see Japanese Laid-Open PatentApplication Publication No. 2006-229901).

The ultrasound element according to Japanese Laid-Open PatentApplication Publication No. 2006-229901 is provided with a piezoelectricvibrator in which a piezoelectric thin film is sandwiched by metalelectrode films on a membrane. According to an ultrasound element ofsuch description, a voltage is applied on an upper-layer and alower-layer metal electrode film, whereby the piezoelectric thin film iscaused to vibrate, the membrane on which the piezoelectric thin film isformed is also caused to vibrate, and ultrasound is produced.

SUMMARY

In an instance in which an ultrasound element such as that shown inJapanese Laid-Open Patent Application Publication No. 2006-229901 ismanufactured, generally, a lower-layer metal electrode film is formed onthe membrane, and a piezoelectric thin film is formed on a layer abovethe lower-layer film; then, the piezoelectric thin film is subjected toan etching treatment and thereby patterned to a predetermined shape.Similarly, when an upper-layer metal electrode film is formed, the metalelectrode film is formed on a layer above the lower-layer metalelectrode film and piezoelectric thin film, and the metal electrode filmis subjected to etching treatment and thereby patterned to apredetermined shape. However, according to a method of such descriptionin which etching is repeatedly performed, during etching of thepiezoelectric thin film and during etching of the upper-layer metalelectrode film, the lower-layer metal electrode film is also subjectedto etching (i.e., over-etching), and the film thickness dimension of thelower-layer metal electrode film is reduced. Thus, when the filmthickness dimension of the metal electrode film is reduced, theelectrical resistance is increased, and problems are presented in that,for example, electricity consumption is increased, the sound pressure ofthe ultrasound output is reduced, and control in a high-frequency regionbecomes difficult.

In view of the above-mentioned problems, an object of the presentinvention is to provide a piezoelectric element, a piezoelectric sensor,an electronic device, and a method for manufacturing the piezoelectricelement, in which the electrical resistance of an electrode can bereduced.

A piezoelectric element according to a first aspect includes a supportbody, a lower electrode layer, a first piezoelectric layer, an upperelectrode layer and a second piezoelectric layer. The support bodyhaving a displacing part that is capable of undergoing displacement in athickness direction. The lower electrode layer has a lower mainelectrode body and a lower electrode wire part, the lower main electrodebody being provided on the support body in a region inside an outerperipheral edge of the displacing part in a plan view when the supportbody is viewed in the thickness direction of the displacing part, andthe lower electrode wire part being connected to the lower mainelectrode body and provided across a region outside and the regioninside the outer peripheral edge of the displacing part. The firstpiezoelectric layer is provided on the lower main electrode body in theregion inside the outer peripheral edge of the displacing part in theplan view. The upper electrode layer is provided across the regionoutside and the region inside the outer peripheral edge of thedisplacing part in the plan view, at least a part of the upper electrodelayer being layered on the first piezoelectric layer and insulated fromthe lower electrode layer. The second piezoelectric layer is provided onthe support body to cover at least a part of the lower electrode wirepart.

According to an example of a configuration of the support body havingthe displacing part of the above described aspect of the presentinvention, a through-hole, a recess, or another opening part is formedon, e.g., a substrate, and a supporting film is formed so as to blockthe opening part, thereby forming a displacing part in which thesupporting film on the opening part is capable of being displaced alonga direction of the film thickness. According to another possibleconfiguration, the displacing part is held on the opening part such asthat described above formed on the substrate, with a bridging partinterposed therebetween. Another possible configuration is a displacingpart in which, e.g., a concave groove is formed on the support body, anda bottom part of the concave groove is capable of being displaced in athickness direction. According to another possible configuration, athrough-hole, a concave groove, or another opening part is formed on asubstrate; an elastic member that has a larger elasticity and deflectsmore readily than the substrate is joined to the opening part; and theelastic member is allowed to undergo displacement. Other possibleconfigurations of the displacing part include one in which the entiretyof the outer peripheral edge of the displacing part is held, or theouter peripheral edge is held at equally spaced intervals, to a mainbody portion of the support body so that the amount of displacement of acenter point is maximized; or one in which one end part of thedisplacing part is held to the main body portion of the support body sothat the amount of displacement of another end part is maximized.

In this aspect, the first piezoelectric layer is layered on the lowermain electrode body of the lower electrode layer, and the secondpiezoelectric layer is layered on at least a part of the lower electrodewire part of the lower electrode layer. The lower electrode layer isthereby covered by the first piezoelectric layer or the secondpiezoelectric layer, making it possible to prevent the lower electrodelayer from being subjected to over-etching during formation of thepiezoelectric layer or the upper electrode layer of the piezoelectricelement, inhibit any increase in the electrical resistance of the lowerelectrode layer, and provide a piezoelectric element having a lowelectrical resistance. In a piezoelectric element having a lowelectrical resistance of such description, when a voltage is appliedbetween the lower electrode layer and the upper electrode layer and thedisplacing part is caused to vibrate, a vibration having a largevibration width can be obtained using a low voltage, and a contributiontowards reducing energy consumption can be made. Also, in an instance inwhich the amount of displacement of the supporting film is measured fromthe size of an electrical current produced by the first piezoelectriclayer, a low electrical resistance in the lower electrode wire partmakes it possible to inhibit loss of electrical current produced by thefirst piezoelectric layer and to detect the displacement of thesupporting film to a high degree of accuracy.

Although the lower electrode layer may be formed so as to have a largeinitial thickness dimension in order to account for over-etching of thelower electrode layer as described above, a problem is presented in suchan instance in that a portion on which the piezoelectric layer is formedas a layer is not subjected to over-etching, and the thickness dimensionof the lower electrode layer is therefore increased, and the totalthickness dimension of a portion in which the piezoelectric layer andthe upper electrode layer are layered is increased. In contrast, in thisaspect of the present invention, it is possible to set the filmthickness dimension of the lower electrode layer without having toaccount for increased electrical resistance or uneven film thicknesscaused by over-etching of the lower electrode layer, and to reduce thethickness of the piezoelectric element.

It is also possible to form the second piezoelectric layer, formed fromthe same material as the first piezoelectric layer, on the lowerelectrode wire part. In such an instance, the second piezoelectric layercan be formed at the same time as the first piezoelectric layer.Therefore, compared to an instance in which a protective layer oranother layer for protecting the lower electrode wire part is separatelyused, the piezoelectric element can be manufactured in a simpler manner,and the manufacturing cost can be reduced.

According to the piezoelectric element as described above, the secondpiezoelectric layer is preferably formed at a position that does notoverlap with the outer peripheral edge of the displacing part in theplan view.

In an instance in which the displacing part is caused to displace incoordination with the vibration of the first piezoelectric layer, or inan instance in which the displacing part is caused to displace due to anexternal stress, forming the edge part of the displacing part so as tohave a small film thickness dimension makes it possible to increase theamount of displacement of the displacing part. In this aspect of thepresent invention, since the second piezoelectric layer is provided at aposition that does not overlap with the edge part of the displacingpart, the thickness dimension of the displacing part near the edge partdoes not increase. Therefore, even in an instance in which thedisplacing part is caused to displace due to vibration of the firstpiezoelectric layer, or in an instance in which the displacing part iscaused to displace due to an external force, the amount of displacementof the displacing part can be increased. Therefore, in an instance inwhich, e.g., the displacing part is caused to vibrate and ultrasound isproduced, the width of vibration of the displacing part can be increasedusing a low voltage, and an ultrasound having an even higher soundpressure can be produced, compared to an instance in which, e.g., thesecond piezoelectric layer is also layered on the edge of the displacingpart. Also, in an instance in which ultrasound is received, it ispossible to cause the ultrasound that is received to cause a largevibration in the displacing part, and it is therefore possible toincrease the reception sensitivity, and to detect the ultrasound to ahigh degree of accuracy.

The piezoelectric element as described above may further have a wiringlayer provided on the second piezoelectric layer. According to thisaspect of the present invention, forming the wiring layer on thepiezoelectric element makes it possible to separate the wiring layer andthe lower electrode layer. In an instance in which a plurality of wiringpatterns are formed on the same planar substrate, there is a possibilityof the size of the substrate or other factors causing the line width ofeach of the wiring patterns to be restricted and increasing theelectrical resistance. In contrast, in this aspect of the presentinvention, the wiring layer is also formed on the second piezoelectriclayer, thereby making it possible to form a wiring pattern on thesubstrate and the second piezoelectric layer so as to have a two-layeredstructure. Therefore, it is possible to reduce the size of the substrateas well as to prevent the electrical resistance from increasing,compared to an instance in which a plurality of wiring patterns areformed on the same substrate.

The wiring layer may provide an electrical connection between twoseparate points on the lower electrode wire part.

In this aspect, the wiring layer provides an electrical connectionbetween two separate points on the lower electrode layer. Therefore, itis possible to pass an electrical current through each of the lowerelectrode layer and the wiring layer between the two points on the lowerelectrode layer, and the electrical resistance can be further reduced.

In the piezoelectric element as described above, it is preferable thatthe lower electrode wire part includes an element connection wiring,provided across the region inside and the region outside the outerperipheral edge of the displacing part in the plan view, the elementconnection wiring connecting to the lower main electrode body, and alower electrode wiring provided in the region outside the outerperipheral edge of the displacing part in continuation with the elementconnection wiring, the lower electrode wiring having a smaller widththan that of the element connection wiring in the plan view. The secondpiezoelectric layer preferably covers the lower electrode wiring.

In this aspect, the second piezoelectric layer covers a portion of thelower electrode wire part that is the lower electrode wiring having asmall line width.

The electrical resistance of the lower electrode wire part decreaseswith an increase in the line width dimension. Therefore, the lowerelectrode wire part is preferably formed so as to have a large linewidth. However, when the piezoelectric element is actually arranged onthe substrate, there are instances in which the lower electrode wiringcannot be provided so as to have a sufficient line width, and the linewidth is smaller than that of the element connection wiring, owing toother elements and their wiring patterns. In such an instance, if thelower electrode wiring is subjected to over-etching when patterning isperformed on the piezoelectric layer or the upper electrode, theresistance of the lower electrode wiring increases. In contrast,according to this aspect of the present invention, the secondpiezoelectric layer is layered on the lower electrode wiring having asmaller line width as described above. Therefore, the lower electrodewiring is not subjected to over-etching when patterning is performed onthe piezoelectric layer or the upper electrode, and the electricalresistance can be prevented from increasing.

A piezoelectric sensor according to another aspect includes a pluralityof the piezoelectric elements of above description, wherein thepiezoelectric elements are arranged in an array.

In this aspect of the present invention, the piezoelectric sensorincludes a plurality of the piezoelectric elements arranged in an array.As described above, in each of the piezoelectric elements, a part of thelower electrode layer is covered by the second piezoelectric layer, andan increase in electrical resistance due to over-etching can thereforebe inhibited. Therefore, in an instance in which, e.g., the supportingfilm is caused to vibrate and ultrasound is produced, ultrasound havinga large sound pressure (i.e., a large vibration width) can be producedwith a low power consumption. In an instance in which, e.g., ultrasoundis received using the supporting film and an ultrasound signal isdetected, a large electrical signal (i.e., a large current) can beoutputted, and the detection accuracy can be increased.

In a piezoelectric sensor of such description, a lower electrode wirepart for providing a connection with each of the piezoelectric elementsis necessary. In an instance in which a small piezoelectric sensor isformed, the line width of each of the lower electrode wire parts isrestricted and made smaller. In such an instance, the electricalresistance of each of the lower electrode wire parts increases. In aninstance in which the second piezoelectric layer is not formed above thelower electrode wire part, there is a possibility of the lower electrodewire part being subjected to over-etching, thereby increasing theelectrical resistance. In contrast, according to this aspect of thepresent invention, the second piezoelectric layer is also formed on thelower electrode wire part having a small line width as described above,making it possible to prevent the resistance from increasing when thepiezoelectric layer and the upper electrode layer are subjected topatterning.

An electronic device according to another aspect includes thepiezoelectric element such as that described above or the piezoelectricsensor such as that described above.

According to this aspect, in the piezoelectric element provided to theelectronic device, a part of the lower electrode layer is covered by thesecond piezoelectric layer, and it is possible to inhibit an increase inelectrical resistance due to over-etching, drive the displacing partusing low electrical power, reduce any loss in an electrical signal fromthe displacing part, and reduce the thickness of the piezoelectricelement, as described above. Therefore, in the electronic deviceprovided with the piezoelectric element as described above or with thepiezoelectric sensor installed with the piezoelectric element, it isalso possible to drive the displacing part using low electrical powerand reduce any loss in an electrical signal from the displacing part,thereby making it possible to reduce power consumption. Also, since thethickness of the piezoelectric element can be reduced, it is possible tocontribute towards reducing the size of the electronic device.

A method for manufacturing a piezoelectric element according to anotheraspect includes: patterning a lower electrode layer on a support bodywith the support body having a displacing part that is capable ofundergoing displacement in a thickness direction, and a lower electrodelayer having a lower main electrode body and a lower electrode wirepart, the lower main electrode body being provided in a region inside anouter peripheral edge of the displacing part in a plan view when thesupport body is viewed in the thickness direction of the displacingpart, and the lower electrode wire part being connected to the lowermain electrode body and provided across a region outside and the regioninside the outer peripheral edge of the displacing part; layering on thelower electrode layer a piezoelectric layer including a firstpiezoelectric layer and a second piezoelectric layer; performing anetching treatment outside a region in which the first piezoelectriclayer is to be formed and a region in which the second piezoelectriclayer is to be formed, and forming the first piezoelectric layer and thesecond piezoelectric layer so that the first piezoelectric layer isprovided on the lower main electrode body in the region inside the outerperipheral edge of the displacing part in the plan view, and the secondpiezoelectric layer is provided on the support body so as to cover atleast a part of the lower electrode wire part; layering an upperelectrode precursor layer; and performing etching and patterning of theupper electrode precursor layer so that the upper electrode layer isprovided across the region outside and the region inside the outerperipheral edge of the displacing part in the plan view, at least a partof the upper electrode layer being layered on the first piezoelectriclayer and insulated from the lower electrode layer.

According to this aspect, after the lower electrode patterning step, apiezoelectric layer layering step, in which a piezoelectric layer islayered, is performed; the piezoelectric layer being for forming thesecond piezoelectric layer and the first piezoelectric layer; the secondpiezoelectric layer covering at least a part of the lower electrode wirepart of the lower electrode layer, and the first piezoelectric layerbeing layered on the lower main electrode body of the lower electrodelayer. After the piezoelectric layer layering step, the piezoelectriclayer patterning step is performed, wherein the piezoelectric layer issubjected to etching, and the first piezoelectric layer on the lowermain electrode body and the second piezoelectric layer covering at leasta part of the lower electrode wire part are formed. After thepiezoelectric layer patterning step, an upper electrode precursor layerlayering step and the upper electrode precursor layer patterning stepare performed, and the upper electrode layer is formed white anyincrease in the electrical resistance of the lower electrode layer isinhibited.

As with the aspects of the invention described above, manufacturing thepiezoelectric element according to the manufacturing method describedabove makes it possible to inhibit any increase in the electricalresistance of the lower electrode layer. Also, since it is possible toform the first piezoelectric layer and the second piezoelectric layer atthe same time, the manufacturing process can be made simpler compared toa method in which, e.g., a protective film for protecting the lowerelectrode layer is separately formed.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a plan view of a piezoelectric element according to a firstembodiment of the present invention;

FIG. 2 is a cross-section view of the piezoelectric element according tothe first embodiment;

FIGS. 3A to 3D are cross-section views showing a part of a process formanufacturing the piezoelectric element;

FIGS. 4A to 4D are cross-section views showing a remaining part of theprocess for manufacturing the piezoelectric element;

FIG. 5 is a cross-section view of a piezoelectric element according to asecond embodiment of the present invention;

FIG. 6 is a plan view of a lower electrode wire part of thepiezoelectric element according to an example of a modification of thesecond embodiment, viewed from a thickness direction of the substrate;

FIG. 7 is a cross-section view along line A-A in FIG. 6;

FIG. 8 is a cross-section view along line B-B in FIG. 6;

FIGS. 9A and 9B are views showing a piezoelectric element according to athird embodiment of the present invention, where FIG. 9A is a plan viewand FIG. 9B is a cross-section view;

FIG. 10 is a plan view showing a part of an ultrasound sensor accordingto a fourth embodiment of the present invention;

FIG. 11 is a schematic perspective view showing a configuration of a PDAaccording to a fifth embodiment; and

FIG. 12 is a schematic perspective view showing a configuration of anultrasound sensor provided to the PDA.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

A configuration of a piezoelectric element according to a firstembodiment of the present invention will now be described with referenceto the accompanying drawings.

Configuration of Piezoelectric Element

FIG. 1 is a plan view of a piezoelectric element according to the firstembodiment.

FIG. 2 is a cross-section view of the piezoelectric element according tothe first embodiment.

In FIG. 1, a piezoelectric element 10 comprises a substrate 11 on whichan opening part 111 is formed; a supporting film 12 formed on thesubstrate 11 across an interior and an exterior of the opening part 111;a lower electrode layer 20 formed on the supporting film 12; a firstpiezoelectric layer 30 formed on an inside of the opening part 111; asecond piezoelectric layer 40 formed on an outside of the opening part111; and an upper electrode layer 50 formed across the interior and theexterior of the opening part 111. The substrate 11 and the supportingfilm 12 form a support body of the present invention. A membrane 121,which is a region of the supporting film 12 that blocks the opening part111, forms a displacing part of the present invention.

The present embodiment shows an example in which the supporting film 12is formed on the substrate 11 having an opening part 111, which is athrough-hole; and the support body is provided with a membrane 121,which is the displacing part. However, the present embodiment is notlimited to that described above. According to an example of anotherpossible configuration, the opening part 111 is a concave groove,wherein the supporting film 12 blocks an opening of the concave grooveopening part 111. Another possible configuration is a support body inwhich a concave groove is formed on the substrate 11 and a bottom partof the concave groove forms the displacing part.

Also, although there is shown an example in which the support body isformed from the substrate 11 and the 12, according to another possibleconfiguration, an insulating film or another layer is provided on alayer above the supporting film 12, and the lower electrode layer 20 isprovided on the other layer.

The piezoelectric element 10 can be used as, e.g., an ultrasoundtransmission element in which a voltage is applied to the firstpiezoelectric layer 30, thereby causing the supporting film 12 tovibrate and ultrasound to be outputted; an ultrasound reception elementin which the supporting film 12 receives ultrasound and the firstpiezoelectric layer 30 outputs an electrical signal corresponding tovibration; a stress detection element for detecting stress applied tothe supporting film 12 according to an electric signal outputted by thefirst piezoelectric layer 30; or a driving force generation element fordriving the first piezoelectric layer 30 and imparting a driving forceto a target object that comes into contact with the supporting film 12.In the present embodiment, a description is given for an example inwhich the piezoelectric element 10 is made to function as an ultrasoundtransmission element.

The substrate 11 is formed from, e.g., a silicon or anothersemiconductor-forming material that can be readily machined by, e.g.,etching. The opening part 111 formed on the substrate 11 is preferablyformed so as to be circular in the plan view. Stress with respect todeflection of the membrane 121, which is a part of the supporting film12 on the inside of the opening part 111, can thereby be made uniform.

Specifically, in an instance in which, e.g., the opening part 111 isformed so as to be, e.g., rectangular, and the first piezoelectric layer30 is formed at a center part of the rectangle, the degree to which aregion of the supporting film 12 readily undergoes deflection differsfrom one region of the supporting film 12 to another even at positionsat which the respective distance from a center point of the membrane 121is equal. In contrast, in an instance such as in the present embodimentin which a circular opening part 111 is formed, the distance from thecenter point of the membrane to an edge part 111A of the opening part111 (that forms an outer peripheral edge of the displacing partaccording to the present invention) is uniform. Therefore, pointssituated at an equal distance from the center point of the membrane 121have the same degree to which the supporting film 12 readily undergoesdeflection, and it is possible to allow the membrane 121 to deflect in auniform manner.

The supporting film 12 is formed on the substrate 11 so as to block theopening part 111. The supporting film 12 has a two-layered structurecomprising, e.g., an SiO₂ layer and a ZrO₂ layer. In an instance inwhich the substrate 11 is an Si substrate, the SiO₂ layer can be formedby subjecting a surface of the substrate to thermal oxidation treatment.The ZrO₂ layer is formed on the SiO₂ layer by, e.g., sputtering oranother method. The ZrO₂ layer is a layer for, e.g., preventingPZT-forming Pb from diffusing into the SiO₂ layer in an instance inwhich PZT is used as the first piezoelectric layer 30 or the secondpiezoelectric layer 40. The ZrO₂ layer also has an effect of improvingthe deflection efficiency with respect to distortion of the membrane121.

The lower electrode layer 20 comprises a lower main electrode body 21formed on the inside of the opening part 111 in the plan view and towhich the first piezoelectric layer 30 is layered on a layer above; alower electrode wire part 22 formed in continuation from the lower mainelectrode body 21 across an interior and an exterior of a regionsurrounded by the edge part 111A of the opening part 111, the firstpiezoelectric layer 30 not being layered on the lower electrode wirepart 21; and a lower electrode terminal part 23 formed at a distal endpart of the lower electrode wire part 22. Specifically, the lowerelectrode wire part 22 is formed across a region inside to a regionoutside the edge part 111A on the membrane 121.

The first piezoelectric layer 30 is formed as a layer on the lower mainelectrode body 21 of the lower electrode layer 20. Formation of thefirst piezoelectric layer 30 is performed by forming, e.g., PZT (leadzirconate titanate) into the shape of a film. Although PZT is used asthe first piezoelectric layer 30 in the present embodiment, any materialmay be used as long as the material is capable of contracting in anin-plane direction under an impressed voltage. For example, leadtitanate (PbTiO₃), lead zirconate (PbZrO₃), or lead lanthanum titanate((Pb,La)TiO₃) may be used.

The first piezoelectric layer 30 is subjected to a voltage applied tothe lower main electrode body 21 and the upper electrode layer 50described further below, thereby causing the first piezoelectric layer30 to contract in the in-plane direction. One surface of the firstpiezoelectric layer 30 is joined to the supporting film 12 with thelower main electrode body 21 interposed therebetween. However, onanother surface, although the upper electrode layer 50 is formed, noother layers are formed on the upper electrode layer 50. Therefore, thefirst piezoelectric layer 30 does not readily contract on a side towardsthe supporting film 12, and readily contracts on a side towards theupper electrode layer 50. Therefore, when a voltage is applied to thefirst piezoelectric layer 30, a convex deflection is formed on a sidetowards the opening part 111, causing the membrane 121 to be deflected.Therefore, adding an AC current to the first piezoelectric layer 30causes the membrane 121 to vibrate in a film thickness direction, andthe vibration of the membrane 121 causes ultrasound to be outputted fromthe opening part 111.

The upper electrode layer 50 is patterned into a positional arrangementwhere a part of the upper electrode layer 50 is layered on the firstpiezoelectric layer 30 in the plan view and insulated from the lowerelectrode layer 20. Specifically, the upper electrode layer 50 comprisesan upper main electrode body 51 layered on the first piezoelectric layer30; an upper electrode wire part 52 formed in continuation from theupper main electrode body 51 across the interior and the exterior of theopening part 111 in the plan view and extending in a different directionto the lower electrode wire part 22; and an upper electrode terminalpart 53 formed at a distal end part of the upper electrode wire part.

A region of the first piezoelectric layer 30 that overlaps with both ofthe upper electrode layer 50 and the lower main electrode body 21represents a region that contracts under application of a voltage.

The second piezoelectric layer 40 is formed from PZT, which is the samematerial as that used for the first piezoelectric layer 30. The secondpiezoelectric layer 40 is formed at a region further outwards from theopening part 111 of the supporting film 12 so as to cover the lowerelectrode wire part 22 of the lower electrode layer 20. Specifically,the second piezoelectric layer 40 is formed so as to cover a portion ofthe lower electrode wire part 22 between an end part position 22A, whichis separated from the edge part 111A of the opening part 111 on thesupporting film 12 by a predetermined distance at which the deflectionof the membrane 121 is not affected, and a part 22B where a connectionis present between the lower electrode terminal part 23 and the lowerelectrode wire part 22. The end part position 22A is separated from theedge part 111A by a predetermined distance because in an instance inwhich the second piezoelectric layer 40 is formed so as to overlap theedge part 111A of the opening part 111, the membrane 121 increases instiffness with respect to deflection, and the sound pressure of theultrasound output decreases. Further preferably, the secondpiezoelectric layer 40 is formed on a portion of the lower electrodewire part 22 between an end part position 22A, at which the distance Lfrom the opening part 111A of the opening part 111 satisfies thefollowing equation (1) when t represents the thickness dimension of thesupporting film 12, and the connecting part 22B.Equation (1)L>5t (1)

This is because when the membrane 121 of the supporting film 12undergoes deflection, a moment is generated in the supporting film 12 sothat the arm part 12 moves into the opening part 111. The moment causesa portion of the supporting film within a distance of 5t from the edgepart 111A of the opening part 111 in the plan view to be subjected to atensile force. Therefore, if the second piezoelectric layer 40 is formedwithin the distance range, a resistance is generated when the membrane121 undergoes deflection, and the sound pressure of the ultrasound isreduced. In contrast, the effect described above does not occur at adistance at or greater than 5t from the edge part 111A of the openingpart 111 in the plan view, and it is possible to cause the membrane 121to deflect to a sufficient degree. In contrast, if the position at whichan end part of the second piezoelectric layer 40 is formed is too farfrom the opening part 111, the area of exposure of the lower electrodewire part 22 is larger. Therefore, when the first and secondpiezoelectric layers 30, 40 are being patterned, and when the upperelectrode layer 50 is being patterned, the exposed portion of the lowerelectrode wire part 22 may be subjected to over-etching, and electricalresistance may be increased. Therefore, most preferably, the secondpiezoelectric layer 40 is formed at a position so as to cover the lowerelectrode wire part 22 between a location separated from the edge part111A of the opening part 111 by a distance of 5t and the part 22B wherea connection is present between the lower electrode terminal part 23 andthe lower electrode wire part 22.

The second piezoelectric layer 40 is not formed on the lower electrodeterminal part 23, because wiring for applying a voltage to the firstpiezoelectric layer 30 is connected to the lower electrode terminal part23.

Method for Manufacturing Piezoelectric Element

A method for manufacturing a piezoelectric element as described abovewill now be described with reference to the accompanying drawings.

FIGS. 3 and 4 are cross-section views showing a process formanufacturing the piezoelectric element.

In order to manufacture the piezoelectric element 10, first, as shown inFIG. 3A, the substrate 11 (Si) is subjected to thermal oxidationtreatment, and an SiO₂ layer is formed on a surface of the substrate 11.A Zr layer is sputtered on the SiO₂ layer, and caused to oxidize,whereby a ZrO₂ layer is formed. The supporting film 12 having athickness dimension of, e.g., 3 μm is thereby formed.

Next, the lower electrode layer 20 is formed on one surface side of thesubstrate 11 by, e.g., sputtering. There are no specific limitations onthe material used for the lower electrode layer 20 as long as the filmis electroconductive. In the present embodiment, a Ti/Ir/Pt/Timultilayer structure film is used, and the lower electrode layer 20 isuniformly formed so that the film thickness is, e.g., 0.2 μm after thepiezoelectric layer is baked.

Then, using, e.g., photolithography, a resist is formed on the lowerelectrode layer 20 at a position at which the lower main electrode body21 and the lower electrode wire part 22 are to be formed. Next,patterning is performed by removing, using etching, a region of thelower electrode layer at which the resist has not been formed, and thelower main electrode body 21, the lower electrode wire part 22, and thelower electrode terminal part 23 are formed as shown in FIG. 3B (i.e.,lower electrode patterning step).

Next, as shown in FIG. 3C, a piezoelectric layer 60 formed from PZT isformed as a layer on one surface of the substrate 11 where the lowerelectrode layer 20 has been patterned. In the formation of thepiezoelectric layer 60, MOD (metal organic decomposition) is used, andtwelve layers of film are formed so that the total thickness dimensionis, e.g., 1.4 μm (i.e., piezoelectric layer layering step).

Then, using, e.g., photolithography, a resist is formed on thepiezoelectric layer 60 at a position at which the first piezoelectriclayer 30 and the second piezoelectric layer 40 are to be formed, andpatterning is performed by removing, using etching, a region at whichthe resist has not been formed. The first piezoelectric layer 30 isthereby formed on the lower main electrode body 21, and the secondpiezoelectric layer 40 is formed on the lower electrode wire part 22, asshown in FIG. 3D (i.e., piezoelectric layer patterning step).

During the piezoelectric layer patterning step, the lower electrodelayer 20 is not subjected to etching at regions at which the firstpiezoelectric layer 30 and the second piezoelectric layer 40 are to beformed. Therefore, disadvantages such as an increase in electricalresistance do not occur.

When the piezoelectric layer 60 is subjected to etching, over-etchingmay occur on a portion of the lower electrode wire part 22 formed in aregion on the opening part 111 in which the first piezoelectric layer 30is not provided, and on a portion of the lower electrode wire part 22within a range of distance L of 5t from the edge part 111A of theopening part 111 (in the present embodiment, since t=3 μm, L=15 μm).Nevertheless, since the portions subjected to over-etching represent anextremely small range relative to the entirety of the lower electrodewire part 22, even when the electrical resistance in these portionsincreases, there are no significant effects.

Next, as shown in FIG. 4A, the upper electrode precursor layer 50A isuniformly formed on one surface of the substrate 11 by, e.g., bysputtering. As with the lower electrode layer 20, any material havingelectroconductivity may be used for an electroconductive film formingthe upper electrode precursor layer 50A; however, in the presentembodiment, an Ir film is used, and is formed so that the thicknessdimension is, e.g., 50 nm (i.e., upper electrode precursor layerlayering step).

Then, using, e.g., photolithography, a resist for patterning of theupper main electrode body 51, the upper electrode wire part 52, and theupper electrode terminal part 53 is formed on the upper electrodeprecursor layer 50A, and patterning is performed by removing, usingetching, a region at which the resist has not been formed. Thereby theupper electrode layer 50 is formed as shown in FIG. 4B (i.e., upperelectrode patterning step).

During the upper electrode patterning step, as with the piezoelectriclayer patterning step, the lower electrode layer 20 is covered by thefirst piezoelectric layer 30 and the second piezoelectric layer 40,over-etching of the lower electrode layer 20 is therefore prevented, andthe electrical resistance of the lower electrode layer 20 can beprevented from increasing.

Next, the thickness dimension of the substrate 11 is adjusted. As shownin FIG. 4C, another surface of the substrate 11 (i.e., a surface onwhich ultrasound is outputted) is subjected to, e.g., polishing orcutting, or otherwise machined, the another surface of the substrate 11being disposed opposite one surface on which the lower electrode layer20, the first piezoelectric layer 30, the second piezoelectric layer 40,or the upper electrode layer 50 are formed. Performing cutting orpolishing as described above makes it possible to reduce the amount ofetching required when the opening part 111 is formed. The substrate 11is formed by RIE (reactive ion etching) using an ICP (inductive coupledplasma) etching device. It is preferable that the cutting and/orpolishing is performed so that the thickness dimension of the substrate11 is 200 μm, accounting for the depth dimension to which etching isperformed, stiffness with respect to warpage under membrane stress, andstrength under handling.

In order to form the opening part 111, a resist is formed on the anothersurface of the substrate 11 at locations other than the position atwhich the opening part 111 is to be formed. The resist is formed to athickness of, e.g., 10 μm so as to be capable of withstanding etching ofthe substrate 11. Then, as shown in FIG. 4D, an ICP etching device isused to perform etching on the substrate 11 from the other surface sideto the SiO₂ layer in the supporting film 12.

The piezoelectric element 10 is thereby manufactured.

Operation and Effect of First Embodiment

As described above, in the piezoelectric element according to the firstembodiment, the first piezoelectric layer 30 is formed on the lower mainelectrode body 21, which is a portion of the lower electrode layer 20formed across the interior and exterior of the opening part 111 that isformed inside the opening part 111, and the second piezoelectric layer40 is formed on a portion of the lower electrode wire part 22 that isoutside the opening part 111.

Therefore, it is possible to prevent the disadvantage of the lowerelectrode layer being over-etched and the electrical resistanceincreasing when etching is performed on the piezoelectric layer 60 andthe first piezoelectric layer 30 and the second piezoelectric layer 40are being formed. Accordingly, the amount of expansion and contractionof the first piezoelectric layer 30 can be increased using a lowerelectrical power, and the sound pressure of the ultrasound produced byvibration of the membrane 121 can be increased.

Also, there is no need to take over-etching into account and increasethe thickness dimension of the lower electrode layer 20, and thethickness dimension of the lower electrode layer 20 can be reduced.Therefore, the piezoelectric element 10 itself can be made thinner.

Also, the first piezoelectric layer 30 and the second piezoelectriclayer 40 are formed from the same material, PZT. Specifically, the firstpiezoelectric layer 30 and the second piezoelectric layer 40 can beformed simultaneously using the piezoelectric layer layering step andthe piezoelectric layer patterning step. Compared to an instance inwhich, e.g., another protective film is provided on the lower electrodelayer 20, the manufacturing process can thereby be made simpler, and theconfiguration can be simplified without the need to separately ready aprotective film.

Also, the second piezoelectric layer 40 is formed at a position thatdoes not overlap with the edge part 111A of the opening part 111 in theplan view.

Therefore, the second piezoelectric layer 40 does not generate aresistance when the membrane 121 undergoes deflection. Accordingly,compared to an instance in which the second piezoelectric layer 40 isformed on the edge part 111A of the opening part 111, the membrane 121can be made to vibrate so as to have a larger vibration width.Therefore, even in an instance in which the voltage applied to the firstpiezoelectric layer 30 is low, it is possible to output ultrasoundhaving a large sound pressure.

The second piezoelectric layer 40 is formed so as to cover a portion ofthe lower electrode wire part 22 between the end part position 22A,which is separated from the opening part 111A of the opening part 111 bya distance L that is five times longer than the thickness dimension t ofthe supporting film 12, and the part 22B where a connection is presentbetween the lower electrode terminal part 23 and the lower electrodewire part 22.

When the membrane 121 undergoes deflection, the supporting film 12 issubjected to a moment in a direction of entering the opening part 111.Therefore, a portion of the supporting film 12 near the edge part 111Aof the opening part 111 is subjected to a tensile force towards theopening part 111 and is made to expand and contract. In an instance inwhich the second piezoelectric layer 40 is formed at a position near theedge part of the opening part 111, the expansion and contraction of theportion of the supporting film 12 is restricted, and there is apossibility of the amount of deflection of the membrane 121 beingrestricted. In contrast, by forming the second piezoelectric layer 40 ata position separated by the distance L from the edge part 111A of theopening part 111 as described above, the deflection resistance of themembrane 121 does not increase, and the amount of deflection of themembrane 121 does not decrease. Therefore, compared to an instance inwhich the distance between the edge part 111A of the opening part 111and a position at which the second piezoelectric layer 40 is formed isless than the distance L, ultrasound having a higher sound pressure canbe produced.

Second Embodiment

Next, a piezoelectric element according to the second embodiment of thepresent invention will be described with reference to the accompanyingdrawings.

FIG. 5 is a cross-section view of the piezoelectric element according tothe second embodiment of the present invention.

In the piezoelectric element 10A according to the second embodiment, anauxiliary electrode layer 70, which is a wiring layer, is formed on thesecond piezoelectric layer 40 in the piezoelectric element 10 accordingto the first embodiment.

Specifically, the auxiliary electrode layer 70 is formed on a layerabove the second piezoelectric layer 40 from the connecting part 22B ofthe lower electrode layer 20, and is made to reconnect with the lowerelectrode layer 20 at the end part position 22A of the secondpiezoelectric layer 40.

The auxiliary electrode layer 70 of such description is formed from thesame material as the upper electrode layer 50, and is formedsimultaneously with the upper electrode layer 50 during the upperelectrode patterning step.

Specifically, after the upper electrode precursor layer layering step inwhich the electroconductive film such as that shown in FIG. 4A isformed, a resist is formed during an upper electrode pattern formationstep, the resist being formed in respective positions where the upperelectrode layer 50 is to be formed and where the auxiliary electrodelayer 70 is to be formed. Then, the electroconductive film outside theregions at which the resist has been formed is removed by etching,whereby the auxiliary electrode layer 70 such as that shown in FIG. 5 isformed.

Operation and Effect of Second Embodiment

According to the piezoelectric element 10A of the second embodiment, itis possible to obtain the same operation and effect as those for thepiezoelectric element 10 of the first embodiment, inhibit any increasein electrical resistance of the lower electrode layer 20, and contributetowards reducing the thickness of the piezoelectric element 10A itself.

Also, providing the auxiliary electrode layer 70 makes it possible tofurther reduce electrical resistance in a wiring portion between thelower electrode terminal part 23 and the lower main electrode body 21,and to drive the first piezoelectric layer 30 and produce ultrasoundusing an even lower voltage.

Also, although the piezoelectric element 10A in FIG. 5 shows aconfiguration in which an end part of the auxiliary electrode layer 70is positioned further outwards relative to the edge part 111A of theopening part 111, the configuration is not limited to that shown.According to an example of another possible configuration, the auxiliaryelectrode layer 70 is also formed on a portion of the lower electrodewire part 22 between the end part position 22A of the secondpiezoelectric layer 40 and the first piezoelectric layer 30. Asdescribed above, the upper electrode layer 50 is a layer formed to asufficiently smaller thickness compared to the second piezoelectriclayer 40, the upper electrode layer 50 being formed so as to have athickness dimension of, e.g., 50 nm. The auxiliary electrode layer 70,which is formed at the same time as the upper electrode layer 50, isformed so as to have a thickness dimension that is equal to that of theupper electrode layer 50. Therefore, even if the auxiliary electrodelayer 70 of such description is formed across the interior and theexterior of the opening part 111, the effect on the deflection of themembrane is negligible, and the sound pressure of the ultrasound is notreduced as a result. Also, in an instance in which the auxiliaryelectrode layer 70 is thus formed on the lower electrode wire part 22between the end part position 22A of the second piezoelectric layer 40and the first piezoelectric layer 30, the auxiliary electrode layer 70layered on the lower electrode wire part 22 makes it possible to inhibitan increase in electrical resistance, even in an instance in which thelower electrode wire part 22 between the end part position 22A of thesecond piezoelectric layer 40 and the first piezoelectric layer 30 issubjected to over-etching during the piezoelectric layer patterning stepor the upper electrode patterning step. Therefore, the electricalresistance can be prevented from increasing in a more efficient manner,and ultrasound having a high sound pressure can be produced using a lowvoltage.

Similarly, the auxiliary electrode layer 70 may be formed on the lowerelectrode terminal part 23. In such an instance, the electricalresistance in the lower electrode terminal part 23 can be prevented fromincreasing.

Example of Modification of Second Embodiment

Although the example of the second embodiment described above shows, asa wiring layer, an auxiliary electrode layer 70 for providing aconnection between two points on the lower electrode layer 20 (i.e.,between the end part position 22A and the connecting part 22B), theconfiguration is not limited to that described above. A configurationshown in FIGS. 6, 7, and 8 is also possible.

FIG. 6 is a plan view of a part of a lower electrode wire part 22 of apiezoelectric element according to an example of a modification of thesecond embodiment, viewed from the thickness direction of the substrate11. FIG. 7 is a cross-section view along line A-A in FIG. 6. FIG. 8 is across-section view along line B-B in FIG. 6;

In the piezoelectric element, a second piezoelectric layer 40A having awidth dimension that is smaller than that of the lower electrode wirepart 22 is provided on the lower electrode wire part 22. Also, as shownin FIGS. 6 and 7, an auxiliary electrode layer 70A is provided on thelower electrode wire part 22 as a wiring layer covering the secondpiezoelectric layer 40A.

Therefore, as shown in FIG. 8, the auxiliary electrode layer 70A is alsoin contact with the lower electrode wire part 22 along an outerperipheral edge of the second piezoelectric layer 40A. The auxiliaryelectrode layer 70A and the lower electrode wire part 22 thereby form atube-shaped wiring structure provided with the second piezoelectriclayer 40A at a center, and it becomes possible to further reduce theelectrical resistance in the lower electrode wire part 22.

Third Embodiment

Next, a piezoelectric element according to a third embodiment of thepresent invention will now be described with reference to theaccompanying drawings.

FIGS. 9A and 9B are views showing the piezoelectric element according tothe third embodiment, where FIG. 9A is a plan view and FIG. 9B is across-section view.

While the piezoelectric element 10A according to the second embodimentshows an example in which the auxiliary electrode layer 70 connected tothe lower electrode layer 20 is provided on a layer above the secondpiezoelectric layer 40, in the piezoelectric element 10B, the upperelectrode wire part 52 is formed on a layer above the secondpiezoelectric layer 40.

In the piezoelectric element 10B according to the third embodiment asdescribed above, the second piezoelectric layer 40 is made to functionas an insulating layer, thereby making it possible to use a simpleconfiguration to form a wiring pattern in which the lower electrodelayer 20 and the upper electrode layer 50 cross each other.

Specifically, in an instance in which the piezoelectric element 10B isformed so as to be disposed in, e.g., an array, there are instances inwhich the arrangement of elements on an array substrate require thelower electrode wire part 22 and the upper electrode wire part 52 to beformed so as to cross each other. In such an instance, conventionally,it has been necessary to form an insulating layer separately in order toprevent the lower electrode wire part 22 and the upper electrode wirepart 52 from coming into contact with each other. In contrast, in thepiezoelectric element 10B according to the third embodiment, the upperelectrode wire part 52 is formed on the second piezoelectric layer 40,thereby making it possible for the upper electrode wire part 52 and thelower electrode wire part 22 to cross each other without separatelyforming an insulating layer.

Fourth Embodiment

Next, as a fourth embodiment of the present invention, a descriptionwill be given for an ultrasound sensor provided with a piezoelectricelement such as those described above, with reference to theaccompanying drawings.

FIG. 10 is a plan view showing a part of the ultrasound sensor accordingto the fourth embodiment.

In FIG. 10, the ultrasound sensor 1 is a piezoelectric sensor accordingto the present invention and has an array structure in which a pluralityof piezoelectric elements 10 are arranged in a lattice shape.

An ultrasound sensor 1 of such description makes it possible to controlthe timing of ultrasound output from the piezoelectric elements 10 tofocus the ultrasound onto a desired point. Although the presentembodiment shows an example of an ultrasound transmission array in whicha plurality of piezoelectric elements 10 for ultrasound transmission arearranged on the substrate 11, the piezoelectric element 10 may also bemade to function as, e.g., ultrasound-receiving elements. In such aninstance, a possible configuration is one in which, e.g., half of thepiezoelectric elements 10 arranged in a lattice shape are made tofunction as ultrasound-transmitting elements, and the remaining half aremade to function as ultrasound-receiving elements. Another possibleconfiguration is one in which the piezoelectric elements 10 are made tofunction as ultrasound-transmitting elements and made to transmitultrasound, after which the piezoelectric elements 10 are made tofunction as ultrasound-receiving elements and made to receive reflectedultrasound. Also, while an ultrasound sensor is shown as an example of apiezoelectric sensor, the piezoelectric sensor may be used as, e.g.,pressure-detecting sensor for measuring contact pressure when acontacting object comes into contact with a piezoelectric sensor, or asensor in which each of the piezoelectric elements 10 is sequentiallydriven, thereby imparting a driving force to the contacting object.

According to an ultrasound sensor 1 of such description, the timing oftransmission of ultrasound outputted from each of the piezoelectricelement 10 is varied, thereby causing ultrasound to be focused on adesired position. Therefore, each of the piezoelectric elements 10 isprovided with a lower electrode wire part 22 that is independent of eachother.

Specifically, as shown in FIG. 10, in each of the piezoelectric elements10, the lower electrode wire part 22 connects to the lower mainelectrode body 21, and comprises an element connection wiring 221 formedacross an interior and an exterior of the membrane 121, and a lowerelectrode wiring 222 for providing a connection between the elementconnection wiring 221 and the lower electrode terminal part 23. Since aplurality of lower electrode wirings 222 are formed between therespective membrane 121 of each of the piezoelectric elements 10,reasons related to layout dictate that each of the lower electrodewirings 222 be formed so as to have a smaller line width dimension thanthe element connection wiring 221. Therefore, the lower electrode wiring222 has a larger electrical resistance than the lower electrode wiring222. In the ultrasound sensor 1 of such description, in an instance inwhich the lower electrode wiring 222 is subjected to over-etching whenthe piezoelectric body and the upper electrode layer 50 in each of thepiezoelectric element 10 are being formed, the electrical resistanceincreases further, and there is a need to apply a high voltage for thepiezoelectric element 10 to output ultrasound having a desired soundpressure. In such an instance, drive control of the piezoelectricelement 10 becomes difficult, particularly in the high-frequency region.However, in the present embodiment, the second piezoelectric layer 40 isformed on the lower electrode wiring 222 where the line width dimensionis smaller than in the element connection wiring 221. Therefore, thelower electrode wiring 222 is not subjected to over-etching duringsensor manufacture, and the electrical resistance can be inhibited fromincreasing.

Also, according to the ultrasound sensor 1 of the present embodiment, asshown in, e.g., FIG. 10, the upper electrode wire part 52 is formed soas to be used jointly by each of the piezoelectric elements 10 arrangedalong one direction (i.e., the lateral direction as seen in FIG. 10).

As with the third embodiment, the upper electrode wire part 52 is formedon the second piezoelectric layer 40. Therefore, it is possible to forma wiring pattern in which the upper electrode wire part 52 and the lowerelectrode wiring 222 are in close proximity to each other with respectto a plan view without causing the upper electrode wire part 52 and thelower electrode wiring 222 to come into contact with each other. Aconfiguration of such description makes it possible to reduce a spacingbetween each of the arranged piezoelectric elements 10, and to reducethe size of the substrate 11 of the ultrasound sensor 1.

Also, in the example shown in FIG. 10, each of the lower electrodewirings 222 and the upper electrode wire parts 52 is disposed so as tonot overlap in the plan view. The upper electrode wire part 52 and thelower electrode wiring 222 may be provided at overlapping positions,e.g., in the plan view.

The present embodiment showed an example in which the upper electrodewire part 52 is used jointly by a plurality of piezoelectric elements10. However, the lower electrode wiring 222, for example, may be usedjointly. In such an instance, the lower electrode wiring 222 can beformed so as to have a larger line width dimension, and providing thesecond piezoelectric layer 40 makes it possible to prevent the lowerelectrode wiring 222 from being subjected to over-etching duringmanufacture. It is therefore possible to further reliably inhibit anincrease in electrical resistance.

Operation and Effect of Fourth Embodiment

The ultrasound sensor 1 according to the fourth embodiment has an arraystructure in which a plurality of piezoelectric elements 10 arearranged. In an ultrasound sensor 1 of such description, in an instancein which the first swing shaft 22 is formed on the substrate 11, it isnecessary to arrange a plurality of lower electrode wirings 222 betweenthe piezoelectric elements 10, restricting the line width dimension ofthe lower electrode wiring 222, and increasing the electricalresistance. In the ultrasound sensor 1 of such description, in aninstance in which the lower electrode wiring 222 is subjected toover-etching during manufacture, the electrical resistance may increasefurther, the sound pressure of the outputted ultrasound may decrease,and drive control in the high-frequency region may be difficult toperform. However, in the present embodiment, the second piezoelectriclayer 40 is formed on the lower electrode wiring 222, thereby making itpossible to prevent the lower electrode wiring 222 from being subjectedto over-etching during manufacture, and to inhibit an increase in theelectrical resistance.

Also, forming the upper electrode wire part 52 on the secondpiezoelectric layer 40 makes it possible to prevent the lower electrodewiring 222 and the upper electrode wire part 52 from coming into contactwith each other. In addition, it becomes possible to form the lowerelectrode wiring 222 and the upper electrode wire part 52 so as tooverlap with each other in the plan view, reduce the distance betweeneach of the piezoelectric elements 10, and contribute towards reducingthe size of the ultrasound sensor 1.

Fifth Embodiment

Next, as a fifth embodiment, a description will be given for anelectronic device according to the present invention, provided with thepiezoelectric element 10 such as those described above. In the firthembodiment, a PDA (i.e., personal data assistant) is used as an exampleof the electronic device.

FIG. 11 is a schematic perspective view showing a configuration of thePDA according to the fifth embodiment. FIG. 12 is a schematicperspective view showing a configuration of an ultrasound sensorprovided to the PDA.

In FIG. 11, the PDA 100 has a main device body 2 and a display part 3.The display part 3 comprises, e.g., a liquid crystal panel or an organicpanel, and connects to a calculation control part 13 (see FIG. 12)accommodated within the main device body 2. The display part 3 isconfigured so that the calculation control part 13 displays a variety ofoperational images and other information on the display part 3. Anultrasound sensor 1A, which is a piezoelectric sensor according to thepresent invention, is disposed on an outer periphery of the main devicebody 2. As shown in FIG. 12, the ultrasound sensor 1A comprises aplurality of piezoelectric elements 10A for transmitting ultrasound anda plurality of piezoelectric elements 10B for receiving ultrasound. Aswith the ultrasound sensor 1 in the fourth embodiment, the piezoelectricelements 10A, 10B are arranged in an array structure such as that shownin FIG. 10, and the second piezoelectric layer 40 is formed as a layeron a portion of the lower electrode wire part 22 that represents thelower electrode wiring 222 disposed in a region outside the membrane121.

In the PDA according to the firth embodiment of such description, thesecond piezoelectric layer 40 is formed as a layer on a portion of thelower electrode wire part 22 that represents the lower electrode wiring222 disposed in a region outside the membrane 121. Therefore, in theultrasound sensor 1A of such description, the lower electrode wiring 222is not subjected to over-etching during manufacture, and there are noincreases in electrical resistance caused by the over-etching.Therefore, the piezoelectric elements 10A for ultrasound transmissionare capable of transmitting ultrasound having a large sound pressureusing a small driving voltage. The piezoelectric elements 10B forultrasound transmission are capable of inhibiting attenuation ofelectrical signals produced by ultrasound reception. Specifically, itbecomes possible for the ultrasound sensor 1A to transmit and receiveultrasound at a high degree of accuracy, and to reduce power consumptionof the ultrasound sensor 1A.

The PDA provided with the ultrasound sensor 1A of such description isthereby capable of detecting a position of a finger or a touch-pen onthe display part 3 to a high degree of accuracy, and of reducing powerconsumption.

In the fifth embodiment, an input device for the PDA 100 installed withthe ultrasound sensor 1A is shown as an example of application of thepiezoelectric element and the piezoelectric sensor according to thepresent invention; however, the application of the piezoelectric elementand the piezoelectric sensor is not limited to that shown. For example,the piezoelectric element or the piezoelectric sensor of the presentinvention can be applied as an input device for, e.g., a portable gameconsole, a mobile telephone, a PC, an electronic dictionary, or asimilar device. The scope of application is not limited to inputdevices, and also includes, e.g., a cleaning device for cleaning atarget object using ultrasound; a proximity sensor or adistance-measurement sensor installed in, e.g., a robot or a motorvehicle and used to measure a distance to a target object or a speed; ameasurement sensor used for non-destructive inspection of pipes or formonitoring of flow speed of a fluid in a pipe; or any other device forperforming a variety of processes using ultrasound output. The scope ofuse of the piezoelectric element or the piezoelectric sensor is notlimited to transmitting and receiving ultrasound, and also includes,e.g., a Braille display device for displaying Braille using vibration ofthe membrane 121; or a driving device for driving, using vibration ofthe membrane 121, a target object that comes into contact with themembrane 121.

The embodiments described above are not intended to limit the scope ofthe present invention; any modification, improvement, or other change isincluded in the invention within a scope allowing the object of thepresent invention to be achieved.

For instance, there was given an example in which the secondpiezoelectric layer 40 is formed so as to cover a portion of the lowerelectrode layer 20 from the end part position 22A separated by adistance L from the edge part 111A of the opening part 111 to the part22B where a connection is present between the lower electrode terminalpart 23 and the lower electrode wire part 22. However, another possibleconfiguration is one in which a portion between the edge part 111A ofthe opening part 111 and the connecting part 22B is covered. In such aninstance, the resistance against deflection of the membrane 121 canstill be reduced, compared to an instance in which, e.g., the secondpiezoelectric layer 40 is formed across the interior and the exterior ofthe opening part 111.

A configuration in which the second piezoelectric layer 40 is formed ona part of the edge part 111A of the opening part 111 is also possible.For example, the second piezoelectric layer 40 may be formed across theinterior and the exterior of the opening part 111 so as to straddle theedge part 111A of the opening part 111 only where the lower electrodewire part 22 has been formed. In such an instance, no part of the lowerelectrode wire part 22 is exposed to an exterior; and it becomespossible to reliably prevent over-etching when the piezoelectric layer60 and the upper electrode precursor layer 50A are etched, and suppressany increase in electrical resistance in an even more reliable manner.Also, compared to a configuration in which the second piezoelectriclayer 40 is formed around the entire periphery of the edge part 111A ofthe opening part 111, resistance against deflection of the membrane 121does not increase, and it is possible to produce ultrasound having alarge sound pressure.

Another possible configuration is one in which the second piezoelectriclayer 40 is not formed within a range of distance L from the edge part111A of the opening part 111, within which range the secondpiezoelectric layer 40 may interfere with the vibration of the membrane121, but is formed on all other regions.

Although in the present embodiment, there was shown by way of example aconfiguration in which the lower electrode layer 20 is formed on thesupporting film 12, the configuration is not limited thereto. Anotherexample of a possible configuration is one in which the supporting film12 is subjected to etching; an insulating layer or another layer, forexample, is layered on an etched portion; and the lower electrode layer20 is formed on the other layer.

Although the present invention has been described in detail above withreference to preferred embodiments, the invention shall not be limitedthereto. Specifically, the present invention was specificallyillustrated and described, mainly in relation to specific embodiments;however, persons skilled in the art may perform any of a variety ofmodifications or improvements to the above embodiments provided that nodeparture is made from the technical concepts and objects of theinvention.

General Interpretation of Terms

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. Finally, terms of degree such as“substantially”, “about” and “approximately” as used herein mean areasonable amount of deviation of the modified term such that the endresult is not significantly changed. For example, these terms can beconstrued as including a deviation of at least ±5% of the modified termif this deviation would not negate the meaning of the word it modifies.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A piezoelectric element comprising: a supportbody having a displacing part that is capable of undergoing displacementin a thickness direction; a lower electrode layer having a lower mainelectrode body and a lower electrode wire part, the lower main electrodebody being provided on the support body in a region inside an outerperipheral edge of the displacing part in a plan view when the supportbody is viewed in the thickness direction of the displacing part, andthe lower electrode wire part being connected to the lower mainelectrode body and provided across a region outside and the regioninside the outer peripheral edge of the displacing part; a firstpiezoelectric layer provided on the lower main electrode body in theregion inside the outer peripheral edge of the displacing part in theplan view, the first piezoelectric layer being formed at a firstposition that does not overlap with the outer peripheral edge of thedisplacing part in the plan view; an upper electrode layer providedacross the region outside and the region inside the outer peripheraledge of the displacing part in the plan view, at least a part of theupper electrode layer being layered on the first piezoelectric layer andinsulated from the lower electrode layer; and a second piezoelectriclayer provided on the support body to cover at least a part of the lowerelectrode wire part.
 2. The piezoelectric element according to claim 1,wherein the second piezoelectric layer is formed at a second positionthat does not overlap with the outer peripheral edge of the displacingpart in the plan view.
 3. The piezoelectric element according to claim1, further comprising a wiring layer provided on the secondpiezoelectric layer.
 4. The piezoelectric element according to claim 3,wherein the wiring layer provides an electrical connection between twoseparate points on the lower electrode wire part.
 5. The piezoelectricelement according to claim 1, wherein the lower electrode wire partincludes an element connection wiring provided across the region insideand the region outside the outer peripheral edge of the displacing partin the plan view, the element connection wiring connecting to the lowermain electrode body, and a lower electrode wiring provided in the regionoutside the outer peripheral edge of the displacing part, incontinuation with the element connection wiring, the lower electrodewiring having a smaller width than that of the element connection wiringin the plan view, and the second piezoelectric layer covers the lowerelectrode wiring.
 6. A piezoelectric sensor comprising: a plurality ofthe piezoelectric elements according to claim 1 arranged in an array. 7.A piezoelectric sensor comprising: a plurality of the piezoelectricelements according to claim 2 arranged in an array.
 8. A piezoelectricsensor comprising: a plurality of the piezoelectric elements accordingto claim 3 arranged in an array.
 9. A piezoelectric sensor comprising: aplurality of the piezoelectric elements according to claim 4 arranged inan array.
 10. A piezoelectric sensor comprising: a plurality of thepiezoelectric elements according to claim 5 arranged in an array.
 11. Anelectronic device comprising: the piezoelectric element according toclaim
 1. 12. An electronic device comprising: the piezoelectric elementaccording to claim
 2. 13. An electronic device comprising: thepiezoelectric element according to claim
 3. 14. An electronic devicecomprising: the piezoelectric element according to claim
 4. 15. Anelectronic device comprising: the piezoelectric element according toclaim
 5. 16. An electronic device comprising: the piezoelectric sensoraccording to claim 6.